Winter water masses in the Gulf of St. Lawrence

The first 9 years of data collected during a new late wintertime hydrographic survey of the Gulf of St. Lawrence are presented. They show colder conditions than those previously measured from ships that were likely biased toward warmer ice‐free waters. The total volume of cold water (<−1°C) varied interannually from 10 to 15 × 103 km3 and is a good predictor for the following summertime Cold Intermediate Layer index. The volume of cold and saline Labrador Shelf waters that flowed in through the Strait of Belle Isle is estimated using two temperature‐salinity criteria. It exhibits much stronger interannual variability than the total cold water volume, representing from 5% to as much as 30% of all cold surface waters. It was sometimes observed to reach the bottom in Mecatina Trough at more than 200 m depth, where deep waters are isolated from the rest of the gulf.